The present invention relates to a nozzle for a chemical laser and more particularly, the invention relates to a nozzle construction in which, e.g., a fuel and an oxidizer are separately charged into a laser cavity, to be mixed therein under particular thermodynamic conditions to, thereby, become a laser-active medium by a chemical reaction under unique flow conditions that are conducive to very high laser performance.
A typical nozzle construction for a chemical laser consists of a plurality of alternating primary and secondary nozzles, wherein the wall structure, defining and establishing the primary nozzles, includes the secondary nozzles and, possibly, tertiary nozzles for adding diluents. See, for example, U.S. Pat. Nos. 3,688,215, or 3,982,208, or 3,991,384. The primary, slit nozzles are charged with oxidizer gas from a chamber in which that gas is, so to speak, prepared. By way of example, this preparation chamber is a combustion chamber in which heat is developed for dissociating fluorine molecules, or a fluorine compound, into fluorine atoms which will serve as the oxidizer in an HF/DF laser. The primary nozzles cause this oxidizer to be charged into the laser cavity and to expand therein, lowering its temperature and pressure to values required to maintain the requisite population inversion, needed for the laser action, which is produced by chemical reaction.
The secondary nozzles feed fuel, e.g., H.sub.2 and/or D.sub.2, into the laser cavity, to combine with the atomic fluorine; and the resulting molecules will assume a temporary population distribution under which laser action occurs. It is desirable, or even necessary, for a variety of reasons to charge the laser cavity at supersonic speed. For example, the temperature and pressure in the combustion chamber are very high and one needs a very extensive dynamic cooling and pressure reduction of the oxidizer for obtaining and maintaining lasing conditions of the reaction production. Viscous losses occuring in the nozzle structure should be minimized in order to ensure adequate performance. Thus, thermodynamic and flow-dynamic conditions simply dictate that the gas be accelerated to supersonic Mach numbers for obtaining the requisite drop in temperature and pressure. On the other hand, adequate pressure recovery is needed and supersonic flow provides the driving force for pressure recovery to permit speedy discharge of used-up laser medium from the laser cavity. Independently therefrom, a high speed of the oxidizer is desired for obtaining a sufficiently large zone in the laser cavity in which the reaction takes place, the zone in which laser action is to take place should be as large as possible, to minimize high-intensity thermal loading of optical components.
It was found that the known nozzle structures generally are deficient as to some or all the requirements outlined above. Specifically, these known structures are difficult to cool and require complex construction features to provide aerodynamic or diluent cooling, or both. Furthermore, it was found that prior art nozzles do not necessarily provide consistently supersonic flow speeds. Clearly, there is a need for optimizing the thermodynamic-gas-dynamic conditions under which the oxidizer is fed into the laser chamber under conditions which maximize useful lasing action in that chamber.
Certain prior art nozzles provide for a flow expansion and mixing in the same direction, resulting in mutual dependency of these two processes which, in turn, does not permit optimization of either. The three patents mentioned above are not very specific with regard to the nozzle structure. A somewhat modified nozzle structure is disclosed in U.S. Pat. No. 3,942,363; but only rather general, thermodynamic, and flow-dynamic conditions are derivable from this patent.
Gas dynamic lasers do also employ a nozzle structure for mixing gases; but since the combined flow fields do not serve as a zone or region for a chemical reaction, one can derive little from nozzle structures such as those disclosed, e.g., in U.S. Pat. No. 3,891,944 or 4,056,789.